A. Technical Field
The present invention relates to an apparatus and a process for purification of an acrylic acid family. In detail, the subjects of the present invention are: a purification apparatus for obtaining an impurity-removed purified material of high purity in processes for production of acrylic acid and acrylic esters which are used as starting materials for production of various chemical products; and a process for purification of the acrylic acid family with such a purification apparatus.
B. Background Art
Acrylic acid and acrylic esters (which are hereinafter generically referred to as acrylic acid family) are widely used as starting materials for production of various chemical products.
In industrial production of the acrylic acid family, the produced acrylic acid family is purified so as to be appropriate for use purposes and demanded quality of the acrylic acid family. In production of the acrylic acid family, there is a possibility that by-products such as (e.g. maleic acid) (which are formed from propylene used as a starting material) and dimer acid (which is formed in the production process) may be contained as impurities in the produced acrylic acid family. Therefore, a purification step for removing these impurities is needed.
A distillation art is applied to the purification of the acrylic acid family. The purification by the distillation is, for example, carried out as follows: a liquid containing the acrylic acid family is vaporized, and then the resultant vapor containing the acrylic acid family in an increased high proportion and the impurities in a reduced low proportion is retrieved and then condensed, thus purifying the acrylic acid family. As the case may be, the impurities are obtained on the vapor side, and the objective product is obtained on the liquid side.
Various arts are proposed for the purpose of increasing the purification efficiency to thus produce an acrylic acid family of high quality or enhance the productivity.
In particular, because the acrylic acid family is an easily polymerizable substance, there is a problem that its polymer is formed in a purification apparatus to thus adhere to an inner wall surface of the apparatus or clog up the piping. Many arts for solving this problem are proposed.
For example, there is an art in which at least two condensers are set in series with a distillation column, thereby preventing a polymer from forming in the apparatus downstream of the condensers to thus adhere to the apparatus (refer to patent document 1 below).
There is an art in which a vapor-dispersing apparatus is set at a place of connection of a reboiler to a distillation column, thereby preventing the channeling of a vapor in the distillation column to thus prevent a polymer from forming in the distillation column to thus adhere to it, wherein the reboiler heat-reboils a liquid from the distillation column and then circulates it (refer to patent document 2 below).                [Patent Document 1]                    JP-A-131116/2001 (Kokai)                        [Patent Document 2]                    JP-A-254403/2000 (Kokai)                        
In the case where the purification apparatus is large-sized in order to enhance the productivity of the acrylic acid family, there greatly occurs the formation and adhesion of its polymer in the apparatus and, in a bad case, the internal piping of the apparatus may be clogged up with the polymer. Therefore, the operation of the apparatus needs to often be stopped for the work of removing the adhered polymer, so that the production efficiency is deteriorated.
In particular, as to a reboiler having a structure such that many tubes are disposed, a polymer adheres to inner surfaces of the tubes to thus easily cause their clogging and, even if the clogging is not caused, there are disadvantages in that the heat-exchange efficiency is greatly deteriorated, thus resulting in great deterioration of the performance of the entire distillation apparatus.
As to the aforementioned prior arts as described in the patent documents 1 and 2, it is impossible to sufficiently prevent the formation and adhesion of the polymer. Particularly as to the large-sized purification apparatus, even the comparatively-short-term operation undergoes the performance deterioration due to the adhesion of the polymer, and therefore the operation needs to be stopped to carry out the work of removing the polymer.